The microbiome is a dynamic community that can positively and negatively influence host health. Lactobacillus reuteri is a probiotic that has received much attention for its ability to inhibit pathogens such as Salmonella typhimurium, Escherichia coli, and Clostridium difficile. It does so by its unique ability to metabolize glycerol into the antimicrobial compound 3-HPA, which is commonly referred to as reuterin. The ability to secrete reuterin is dependent not only on glycerol availability but also the concentration of glucose. In fact, there appears to be a “goldilocks” ratio between glucose and glycerol as either too much or too little glucose significantly diminishes reuterin production. Since L. reuteri primarily resides in distal regions of the intestine and colon where most of the glucose has already been absorbed, it seems unlikely that reuterin production would be promoted at the physiological level via this mechanism.

Prebiotics are carbohydrates that are indigestible by the host and remain for enzymatic digestion by intestinal probiotics. Inulin and galactooligosaccharides (GOS) are two widely studied prebiotics that are known for their ability to promote the growth of a wide range of Lactobacilli, and have been shown to promote L. reuteri growth to varying degrees. Here, we asked if prebiotics such as inulin and GOS promote the production of reuterin in the absence of glucose. L. reuteri were cultured in TSB with or without glycerol in the presence of glucose, inulin, or GOS and assessed for their ability to produce reuterin. While inulin did not enhance the production of reuterin, GOS induced reuterin production, although 45% less than that of glucose. Moreover, unlike the dosedependence observed with glucose, incubation with GOS induced similar reuterin production regardless of concentration. This suggests that an enzymatic equilibrium may exist where glucose/galactose is cleaved from GOS only as needed by L. reuteri.

Finally, to confirm the biopotency of reuterin production, we cultured S. typhimurium with supernatants from L. reuteri that were grown with various carbohydrates. Supernatant dilutions as low as 1:15 were able to significantly retard growth of S. typhimurium with ratios of 1:1 completely inhibiting growth. Together, these results suggest that prebiotics such as GOS may be able to elicit physiologically relevant production of reuterin, which may shape the flora of the microbiome and reduce incidence and severity of pathological infections. Further, as GOS are particularly abundant in breast milk, it suggests a possible link for early immunoprotection from intestinal pathogens while the infant is still immunologically naïve.